The present invention relates to resin-bonded grinding elements containing diamond grit and more particularly to the use of dual-coated diamond grit therein for both dry grinding and wet grinding cemented carbide workpieces.
Use of metal coated diamond grit embedded in the abrasive section of resin bonded grinding wheels is a well practiced commercial technique for enhancing the grinding operation. Lindstrom (U.S. Pat. No. 3,957,461) proposes such metal coated diamond for use in the grinding section of a resin bonded grinding element wherein the metal coating is taught to form a mechanically strong shell for holding together fractional portions of the diamond particles and for effectively increasing the adhesion between the diamond particles and the resin material. Coatings shown include cobalt, nickel, silver, cadmium, zinc, copper, iron, tin, molybdenum, titanium, manganese, aluminum, chromium, gold, tungsten, zirconium, and platinum group metals. Otopkov (British Pat. No. 1,344,237) proposes to coat diamond or boron nitride abrasive grains with two materials, one of which is silicon and the other of which is a metal selected from copper, silver, gold, aluminum, cobalt, nickel, ruthenium, osmium, iridium, platinum, and certain transition metals. German Auslegeschrift No. 2,218,932 apparently is an equivalent of Otopkov's British Patent. Seal (U.S. Pat. No. 3,528,788) etches the metal coating on the diamond grit for improving the grinding ratio of resin bonded grinding wheels containing the etched grit.
Sioui (U.S. Pat. No. 3,779,727) proposes to incorporate fillers into the resinous material used to formulate resin bonded abrasive tools wherein the fillers include a solid lubricant and a metal which is silver, silver coated copper, or copper powder. The diamond grit or cubic boron nitride (CBN) abrasive further may be coated with conventional metals. As noted by Sioui in "The Evolution of Tests for Diamond Wheel Performance in Dry Tool and Cutter Sharpening," Proceedings: Diamonds in the 80's, pp 131-138, Industrial Diamond Association, Chicago, Ill. (October 13-15, 1980), and in "The Use of Silver in Diamond and CBN Wheels for Dry Grinding Hard Materials", Cutting Tool Engineering, July/August, 1980, pp 8-11; the silver filler in the resin apparently acts as a thermal conductivity agent to remove heat fron the grinding section and workpiece area contacted by the grinding section due to the high thermal conductivity of the conductive metals silver, copper, and silver-coated copper.
Lindstrom (U.S. Pat. No. 3,955,324) proposes agglomerates of metal-coated diamonds for embedding in the grinding section of resin bonded grinding elements wherein the matrix metal of the agglomerates is a metal which possesses good heat conducting ability. Such metals are shown to include nickel, copper, cobalt, and silver or alloys thereof. Naidich (U.S. Pat. No. 4,024,675) proposes such aggregate abrasive grains wherein adhesion agents are added to the metal and abrasive grains to make a porous cake which is sintered and subsequently ground to produce the aggregated abrasive grains. Phaal (U.S. Pat. No. 4,246,006) forms aggregates of diamond particles wherein a powdered metal and the diamond abrasive particles are heated to sinter the metal followed by cooling and crushing of the resulting mass. Suitable metals for producing such agglomerates include copper, silver, tin, nickel, cobalt, and iron or alloys thereof.
Slack (U.S. Pat. No. 4,239,502) dips diamond or CBN in a molten Ag/Mn/Zr brazing alloy which coated particles are brazed onto Mo or W rim portions of grinding wheels. U.S. Pat. No. 2,411,867 mentions silver coated boart.
Finally, commonly-assigned application Ser. No. 264,765, filed May 18, 1981, now abandoned, teaches that dry grinding of cemented metal carbide workpieces and combinations of cemented metal carbide and steel workpieces can be subjected to dry-grinding with decreased power required to rotate the grinding element and increased grinding ratios by using a resin bonded grinding element having coated diamond particles embedded in the grinding surface wherein the diamond particles are coated with a layer of metal consisting essentially of silver. However, when the silver-coated diamond grit is used in wet grinding operations, it does not work as well.
Despite the advance in technology relating to use of metal coated diamond grit in grinding operations, prior metal coated diamond grit is restricted to use in either dry grinding or wet grinding operations depending upon the particular metal used to coat the diamond grit. That is, nickel-coated diamond grit typically is recommended for use in wet grinding cemented carbide workpieces while copper-coated diamond grit is recommended in dry grinding operations. Silver-coated diamond grit, as stated above, has been shown to be superior in dry grinding operations, yet of little value in wet-grinding operations. The present invention is directed to a new universal coating and universally-coated diamond grit for both dry grinding and wet grinding operations.